Fintube welding apparatus

ABSTRACT

An apparatus for mounting and welding fin stock to a tube is disclosed. The apparatus comprises a weld wheel rotatably mounted adjacent to a length of tubing at the point where a length of fin stock is fed onto the peripheral surface of the tubing. The weld wheel comprises a plurality of discs having annular portions spaced therebetween, the space between the discs forming annular pockets for receiving one or more of the fin portions as they are being fed onto the tubing. The sides of the discs extend substantially to the base of the fin stock to engage and adequately support the sides of the fin portions during such feeding. A first electrode is provided to contact the tubing surface, and a second electrode is provided to contact a portion of the weld wheel. The tubing, fin stock, and weld wheel are in continuous metal-to-metal engagement to establish an electrical current path between the two electrodes. A high frequency current is applied through the current path to melt the root of the fin stock and the surface of the tubing immediately prior to their mutual engagement point. As the fin stock and the tubing are drawn together, the annular portions function to apply a forging force to the fin stock to create a fused bond between the fin stock root and the tubing. Because of the lateral support provided by the weld wheel pockets, the wiggling at the base of the fin stock is minimized, thereby creating a stronger weld connection with the tubing.

United States Patent [191 Boose et al.

[45] Mar.'27 1973 Primary Examiner-J. V. Truhe Assistant Examiner-L. A.Schutzman AttorneyJackson & Jones [57] ABSTRACT An apparatus formounting and welding fin stock to a tube is disclosed. The apparatuscomprises a weld wheel rotatably mounted adjacent to a length of tubingat the point where a length of fin stock is fed onto the peripheralsurface of the tubing. The weld wheel comprises a plurality of discshaving annular portions spaced therebetween, the space between the discsforming annular pockets for receiving one or more of the fin portions asthey are being fed onto the tubing. The sides of the discs extendsubstantially to the base of the fin stock to engage and adequatelysupport the sides of the fin portions during such feeding. A firstelectrode is provided to contact the tubing surface, and a secondelectrode is provided to contact a portion of the weld wheel. Thetubing, fin stock, and weld wheel are in continuous metal-to-metalengagement to establish an electrical current path between the twoelectrodes. A high frequency current is applied through the current pathto melt the root of the fin stock and the surface of the tubingimmediately prior to their mutual engagement point. As the fin stock andthe tubing are drawn together, the annular portions function to apply aforging force to the fin stock to create a fused bond between the finstock root and the tubing. Because of the lateral support provided bythe weld wheel pockets, the wiggling at the base of the fin stock isminimized, thereby creating a stronger weld connection with the tubing.

1 1 Claims, 5 Drawing Figures PATENTEUHARZYIQYS SHEET 2 BF 2 FINTUBEWELDING APPARATUS BACKGROUND OF THE INVENTION It has long been customaryto attach fins made of metal to the exterior of tubing used in heatexchanger bundles to increase the effective area for heat transferbetween a fluid flowing through the interior of the tubing and, in mostcases, a liquid or gas across the outside thereof.

The types of fins utilized for attachment to the tubing are normallyclassified in three groups; the flanged fin, the channel fin, and theHype fin. The flanged fin type comprises a major fin portion extendingradially from the tubing and a bottom flanged base orientedperpendicular to the fin portion with the base adapted to be wrapped andattached around the outer surface of the tubing. The channel fin typecomprises a continuous base having a pair of fin portions extendingradially upwardly therefrom to form a U-shaped configuration. The I-typefin comprises a flat fin portion having its lower edge forming thebasefor attachment to the tubmg.

The major fin portion of each of these various fins can be of thecontinuous or segmented type. The continuous fins normally have a smoothcontinuous surface, although they can be perforated to meet certaindesign conditions. The segmented fins comprise a plurality of bladesformed from a continuous fin by cutting a plurality of slits downwardlyfrom the top of the tin. The segmented fins are either oriented parallelto the root portion of the fin or are twisted at an angle thereto in anydesired orientation in order to promote turbulence and increase the heattransfer rates.

These fins may be engaged to the tube in a helical or longitudinalconfiguration with the method of securing the fins to the tubing usuallyaccomplished by some type of welding, brazing, or tension winding.

Although many types of welding methods have been utilized in attachingfins to tubing, a method that has been used extensively is the highfrequency welding process. This process utilizes a forging or pressurewheel rotatably mounted adjacent to a length of rotatable tubing. Alength of fin stock is helically' fed onto the rotating tubing and isbiased against the tubing by the forging or pressure wheel near thepoint of mutual engagement of the fin with the tubing. A pair of silverelectrodes are provided for engaging the base of the fin and the surfaceof the tubing respectively just prior to the above-mentioned mutualengagement point. The electrodes, fin stock and tubing are in continuousengagement to provide an' electrical current path therethrough. A highfrequency current is applied through the path to cause the root of thefin and the tubing surface to melt. The force of the forging or pressurewheel against the fin causes the root of the fin to fuse against thetubing surface. Since space must be provided for enabling the electrodeto contact the fin, the pressure wheel could only contact the top of thefin. For this reason, a ceramic guide is provided to bear against theside of the fin as it is fed onto the tubing to give the fin lateralsupport.

A major advantage of this process is that the speed of producing finnedtubing is greatly increased.

However, the process includes various shortcomings which severely limitits utilization.

One problem with such a system is that for efficient operation, theresistance along the current path must be kept at a minimum. Because ofthis, the silver electrode has to be positioned to contact the tin stockas closely as possible to the point where it engages the tubing surface.As stated previously, this space is provided by extending the pressurewheel only to the tip of the fin stock or just slightly below, leavingone side of he fin stock unsupported except by the ceramic.

However, it has been found that firm lateral support is required for thefin stock as it is being wound onto the tubing surface. This is becauseof the fact that as the fin stock is bent around the tubing, the base ofthe fin is compressed while the tip of the fin is stretched. Thesecompressive forces tend to cause the base of the fin to crimp or wiggleduring such bending. This wiggling movement is detrimental to thecreation of the weld. Utilizing a ceramic guide helps to give somelateral support. However, this support is not completely satisfactory tominimize the crimping and the weld that is created is inferior for manyrequirements.

Another problem involved is the high expense of the silver contacts. Notonly is the initial cost of silver contacts high, but these contactshave a relatively high rate of wear and must be replaced at relativelyshort time intervals. Moreover, because of the fin wiggling movement,other cheaper metals cannot be used because of the high conductivityneeded to ensure a proper flow of current between the fin and theelectrode.

Another problem with the process is that the ceramic guides must bereplaced frequently. This, of course, results in an additional amount ofdown time for the machine.

SUMMARY OF THE lNVENTlON The present invention obviates theabove-mentioned shortcomings by providing an apparatus for mounting andwelding fin stock onto a tube, with the operation thereof being moreefficient and economical and the fintube produced therefrom having asuperior bond therebetween.

The apparatus comprises a rotatable weld wheel mounted adjacent to alength of tubing. The weld wheel includes an annular pocket forreceiving the fin stock and laterally supporting the sides thereof as itis being fed onto the tubing. A pair of electrodes are provided, thefirst electrode contacting the tubing surface while the second electrodecontacts a portion of the weld wheel. The first electrode, tubingsurface, fin stock, weld wheel, and second electrode are in continuousengagement for providing an electrical current path therebetween. A highfrequency current is applied through the path to melt the root of thefin stock and the surface of the tubing immediately prior to theirmutual engagement point. The weld wheel further includes an annularsurface that is adapted to contact the fin stock for applying a forgingforce thereto to create a fused bond therebetween.

A primary advantage of the present invention is that the electrodecontacts the weld wheel instead of the fin stock. Since the rotation ofthe weld wheel is more stable than the movement of fin stock, thesliding engagement between the electrode and the weld wheel is greaterand more continuous than the contact between an electrode and a fin.This enables the electrode to be made of a material having lessconductivity than silver. The preferred embodiment utilizes a copperelectrode. The advantage of utilizing a copper electrode instead of asilver electrode is threefold. Firstly, the initial cost of a silverelectrode is much more than a copper electrode. Secondly, the copperelectrode lasts much longer than a silver electrode. As a result, thereplacement costs are greatly reduced. Thirdly, the added down time forreplacing the silver electrode and the expense involved therewith ismuch greater than if copper electrodes were utilized.

Another advantage of the present invention is that because the weldwheel extends substantially to the base of the fin on both sides thereofthe weld wheel provides all the guidance for the fin. Moreover, suchguidance gives better lateral support to the fins than heretoforepossible to minimize the wiggle at the base of the fin. This produces abetter weld between the fin and the tubing surface. In fact, in a testconducted by the Navy at the Puget Sound Naval Shipyard, the fintubesample tested, which was made in accordance with the present invention,showed no deterioration on the bond between the fin and the tubing.Their conclusion was that the fin attachment method was recommended fortheir installations.

A further advantage of the present invention is that the lateral supportprovided by the weld wheel eliminates any requirement for ceramic guidesor similar lateral support means. This makes the operation much simplerand more easily adaptable to various types of fintube configurations.Moreover, by eliminating ceramic guides in the manufacturing process,the amount of down time for replacing such guides is eliminated.

As a result, the present invention provides a less complex system forproducing fintube of higher quality at a lower cost.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and rnanner of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description, taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a plan view of anapparatus mounting and welding a segmentedchannel fin to a tube;

FIG. 2 is an elevational view, partly in section, of the apparatus ofthe present invention taken along lines 2-2 of FIG. 1; I

FIG. 3 is a plan view of a second embodiment of the present inventionmounting and welding a segmented I- type fin to a tube;

FIG. 4 is a plan view of a third embodiment of the present inventionmounting and welding a pair of continuous I-type fins to a tube; and

FIG. 5 is a plan view of a fourth embodiment of the present inventionmounting and welding a pair of continuous channel fins to a tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring now to the drawings, FIG. 1 shows an apparatus, generallyindicated by arrow 10, for mounting and welding a length of fin stock 20onto a length of tubing 30. The fin stock 20 is U-shaped in crosssection and is conventionally described as a channel fin. A channel finconstruction is described in U. S. Pat. No. 3,550,235 issued Dec. 29,1970. The channel fin 20 is also segmented in the conventional manner toenable the fin stock 20 to be more easily wound onto the surface of thetubing 30. As more clearly shown in FIG. 2, the fin stock 20 is fed ontothe outer surface of the tubing 30 while the tubing 30 is rotating. Thetubing 30 also is moved longitudinally during rotation to enable the finstock 20 to be helically wound thereon. This helical winding is shown inFIG. 1. The apparatus 10 for attaching the fin stock 20 to the tubing 30comprises a weld wheel 40 which is rotatably mounted adjacent' thetubing 30 at the point where the fin stock 20 is fed onto the peripheralsurface thereof. The weld wheel 40 is driven by a motor 41 to rotate atthe same tip speed as the tubing 30. The weld wheel 40 comprises a pairof annular pockets 43 and 45 which are adapted to receive the channelfin 20.

The weld wheel 40 includes three discs 47, 48, and 49 joined together ina side-by-side relationship. The disc 47 and 48 have smaller diameterannular portions 51 and 52 formed thereon and are mounted to besandwiched between the discs to form the aforesaid pockets 43 and 45.The sides of the discs 47, 48, and 49 extend substantially to the baseof the fin stock 20 to engage and adequately support the sides of thefin stock 20 as it is being fed onto the peripheral surface of thetubing 30. The center disc 48 extends entirely within the channel fin 20and is adapted to engage the base portion of the fin 20 to apply a forcethereon. Each of the discs 47, 48, and 49 are preferably made ofberylium 'while the annular portions 51 and 52 can be made of steel forlonger life under the forging force friction.

A first electrode 60 is provided having a surface for contacting theouter peripheral surface of the tubing 30. A second electrode isprovided having a surface for contacting the exterior disc 47 of theweld wheel 40. It should be noted that the fin stock 20, tubing 30, andweld wheel 40 are in a continuous metal-to-metal contact to establish anelectrical current path between the two electrodes 60 and 70.

In operation, a high frequency current is applied through this path asthe fin stock 20 is being fed onto the periphery of the tube 30. Thiscurrent functions to melt the root of the fin stock 20 and the surfaceof the tubing 30 immediately prior to their mutual engagement point. Asthe molten portions of the fin stock 20 and tube 30 are united,'thecenter disc 48 and the annular portions 51 and 52 apply a forging forceto the fin stock 20 to create a fused bond therebetween. As previouslypointed out, the lateral support given by the weld wheel 40, reduces thelateral movement or wiggling of the fin stock 20 as it is being attachedto the tubing 30. This reduction of wiggling creates a much strongerweld between the fin stock 20 and the tubing 30 that was not heretoforepossible.

FIG. 3 illustrates a second embodiment of the present invention whereinan apparatus is utilized to mount and attach a segmented l-type fin 120onto a length of tubing 130. 1 ln this second embodiment, a weld wheel140 is rotatably mounted adjacent to the tubing 130 and comprises a pairof discs 147 and 148 having a smaller diameter segment sandwichedtherebetween to form a pocket 152 for receiving the fin stock 120. As inthe previous embodiment, the discs 147 and 148 extend substantially tothe base of the fin stock 120 to engage and provide adequate support tothe sides thereof. The base of the pocket 152 functions to engage thetip of the fin 120 for applying a forging force thereto. First andsecond electrodes 160 and 170 are provided to respectively contact theperipheral surface of the tube 130 and the exterior disc 147 of the weldwheel 140. As in the previous embodiment, the fin stock 120, tubing 130,and weld wheel 140 are in continuous metal-to-metal contact to establishan electrical current path between the two electrodes 160 and 170.Similarly, a high frequency current is applied via the electrodes 160and 170 through the current path to melt the root of the l-type finstock 120 and the surface of the tubing 130 immediately prior to theirmutual engagement point. As the fin stock 120 and tubing 130 are united,the base of the pocket 152 applies a force to the fin stock 120 tocreate a fused bond therebetween.

FIG. 4 illustrates a third embodiment of the invention in which theapparatus 200 is utilized to attach a pair of continuous Itype fins 220onto the peripheral surface of a tube 230 simultaneously. The weld wheel240 is similar to that shown in the first embodiment and includes twopockets 243 and 245 forined by positioning three discs 247, 248, and 249in a side-byside relationship having a pair of smaller diameter steelwashers 251 and 252 sandwiched therebetween. A pair of electrodes 260and 270 are positioned to respectively contact the tube 230 and thewheel 247 of the weld wheel 240. The disc 247, 248, and 249 extendsubstantially to the bases of the respective fins 220 for lateralsupport. The operation for this embodiment is similar to the previousembodiments. The only difference is that two continuous i-type fins areattached simultaneously thereby doubling the longitudinal speed of thetubing for any given rotational speed.

FIG. 5 shows a fourth embodiment of the invention in which the apparatus300 is utilized to attach a pair of continuous channel fins 320 onto theperipheral surface of a tube 330 simultaneously. The electrode structure360 and 370 is similar to that of the previous'embodiments'The novelstructure in this embodiment lies in the weld wheel 340 which comprisesfive outer discs 347, 348, 349, 350, and 351. Four smaller diametersteel spacer discs 353, 354, 355, and 356 are sandwiched therebetween.The pockets 341, 342, 343, and 344 formed therein function to receivethe pair of channel fins 320 to laterally support the fins 320. Thebases of the pockets function to apply a forging force to the fins 320to create a fused bond between fins 320 and the registering tube surface330. The five outer discs are preferably made of berylium while thespacer discs are preferably made of steel.

As can be seen, the lateral support provided by the weld wheel givesmore than adequate support to the fin stock to substantially reduce thelateral movement of the fin stock as it is being fed onto the surface ofthe fin. As a result, a better weld is achieved.

Moreover, by contacting the weld wheel instead of a prior relativelyunsupported fin, the electrode can be made of copper. This is becausethe lateral movement of the weld wheel is much less than the prior finsthereby enabling a metal electrode of less conductance to be usedinstead of the prior silver electrodes.

It should be noted that various modifications can be made to theapparatus while still remaining within the purview of the followingclaims. For example, the fin receiving pockets in the weld wheel-can beformed within an integral wheel or the weld wheel can be formed fromvarious plates or discs.

What is claimed is:

1. Apparatus for mounting and welding a length of fin stock onto thesurface of a length of tubing comprismg:

means for feeding the fin stock onto the tubing;

a first electrode adapted to contact the tubing;

a source of high frequency potential connected to the first electrode;

a second electrode connected to the source of high frequency potential;and

a force applying weld wheel means for simultaneously bending and weldingthe fin stock to the tubing surface including a first metallic discconnected to the source of high frequency potential through a slidingcontact with the second electrode adjacent the weld point and adapted tocontact one side of the fin stock adjacent its base to both guide thefin stock and provide an electrical contact with the fin stock toconduct a weld current, a metallic pressure roller positioned adjacentthe first disc and adapted to contact the top edge of the fin stock toexert a force against the fin stock to bend the fin stock about the tubesurface and to assist in creating the fused bond with the tubingsurface, and a second metallic disc positioned adjacent the metallicpressure roller and adapted to guidingly contact another side of the finstock.

2. The invention of claim 1 wherein the second metallic disc is thinnerthan the first metallic disc,

whereby the'fin stock can be helically wound closer together withouttouching the second metallic disc than if it was the same thickness asthe first metallic disc.

3. The invention of claim 1 wherein the first and second metallic discsare berylium and the pressure roller is steel and a copper electrodeconnects the first metallic disc with the source of high frequencypotential.

4. The invention of claim 1 wherein the only current applied to the finstock and tube is through the first metallic disc. I

5. The invention of claim 2 wherein the second metallic disc is concavetowards the first metallic disc.

6. The invention of claim 2 wherein a third metallic disc and a secondmetallic pressure roller are positioned between the first and secondmetallic discs to form a pair of annular pockets for receiving the finsof the fin stock.

7. The invention of claim 6 wherein the third metallic disc engages thebase portion of the fin stock during a welding operation.

8. The invention of claim 7 wherein the third metallic disc has a largerdiameter than the first and second metallic discs.

9. The invention of claim 8 wherein fourth and fifth metallic discs andthird and fourth metallic pressure 1 rollers are positioned between thethird and second 11. The invention of claim 10 wherein the metallicdiscs are berylium and the metallic pressure rollers are steel and acopper electrode electrically connects the first metallic disc with thesource of high frequency potential.

1. Apparatus for mounting and welding a length of fin stock onto thesurface of a length of tubing comprising: means for feeding the finstock onto the tubing; a first electrode adapted to contact the tubing;a source of high frequency potential connected to the first electrode; asecond electrode connected to the source of high frequency potential;and a force applying weld wheel means for simultaneously bending andwelding the fin stock to the tubing surface including a first metallicdisc connected to the source of high frequency potential through asliding contact with the second electrode adjacent the weld point andadapted to contact one side of the fin stock adjacent its base to bothguide the fin stock and provide an electrical contact with the fin stockto conduct a weld current, a metallic pressure roller positionedadjacent the first disc and adapted to contact the top edge of the finstock to exert a force against the fin stock to bend the fin stock aboutthe tube surface and to assist in creating the fused bond with thetubing surface, and a second metallic disc positioned adjacent themetallic pressure roller and adapted to guidingly contact another sideof the fin stock.
 2. The invention of claim 1 wherein the secondmetallic disc is thinner than the first metallic disc, whereby the finstock can be helically wound closer together without touching the secondmetallic disc than if it was the same thickness as the first metallicdisc.
 3. The invention of claim 1 wherein the first and second metallicdiscs are berylium and the pressure roller is steel and a copperelectrode connects the first metallic disc with the source of highfrequency potential.
 4. The invention of claim 1 wherein the onlycurrent applied to the fin stock and tube is through the first metallicdisc.
 5. The invention of claim 2 wherein the second metallic disc isconcave towards the first metallic disc.
 6. The invention of claim 2wherein a third metallic disc and a second metallic pressure roller arepositioned between the first and second metallic discs to form a pair ofannular pockets for receiving the fins of the fin stock.
 7. Theinvention of claim 6 wherein the third metallic disc engages the baseportion of the fin stock during a welding operation.
 8. The invention ofclaim 7 wherein the third metallic disc has a larger diameter than thefirst and second metallic discs.
 9. The invention of claim 8 whereinfourth and fifth metallic discs and third and fourth metallic pressurerollers are positioned between the third and second metallic discs toform an additional pair of annular pockets for receiving the fins of thefin stock.
 10. The invention of claim 9 wherein the fifth metallic dischas the same diameter as the third metallic disc.
 11. The invention ofclaim 10 wherein the metallic discs are berylium and the metallicpressure rollers are steel and a copper electrode electrically connectsthe first metallic disc with the source of high frequency potential.